Conventional VTOL/STOL aircraft employ a wide range of aerodynamic approaches to produce their needed vertical lift, forward speed, and stability while providing safe and efficient operation. Invariably, the technical compromises which result from meeting these diverse requirements produce operating aircraft having less than optimum characteristics in one or more important areas. The redeeming feature of air transportation is, of course, speed. However, in the case of helicopters this major advantage is fundamentally limited because of the technical factor of retreating blade stall. This involves the significant loss of lift by the retreating blade (the one turning toward the rear of the aircraft) due to vitiated relative wind, and places a practical upper limit on helicopter speeds.
Attempts to overcome some of the many design compromises of vertical lift systems for aircraft are well represented in the prior art. As a typical example, consider U.S. Pat. No. 4,598,887 to Jordan which discloses a rotary wing craft having two rotor blades for lift and a driven coaxial propeller (fan), both disposed above an essentially vertical air channel. In operation, the air stream generated by the propeller produces torque on guide vanes connected to the main blades, thereby driving the lifting blades.
U.S. Pat. No. 3,563,497 to Holmes discloses a rotorcraft which provides lift by means of a rotor element and a pair of counterrotating secondary rotors, wherein the rotor systems are axially aligned and allow for air flow between them via a vertical air passage. In operation, the thin rotor element may be driven to provide helicopter operation; may be freewheeling to provide autogyro operation; or may be stopped to provide fixed-wing-like operation.
In U.S. Pat. No. 3,103,327 to Parry there is disclosed a somewhat similar helicopter arrangement, including an upper 2-bladed rotor and a counterrotating lower propeller which combine to produce lift and thrust. Other earlier prior art approaches to more generalized vertical lift systems are found in U.S. Pat. Nos. 3,394,906 to Rogers (1966) and 2,980,365 to Yohe (1961).
Significant disadvantages of helicopter-like lift producing airfoils involve their typically low solidity ratios, and their low lift efficiencies for the portions of their airfoils nearest the hub. Solidity ratios (quantity of solid wing--or blade--area relative to the area swept out by the full length rotating elements) for smaller aircraft tend to be the lowest due to their use of two narrow blades. Regarding lift efficiencies, conventional rotary wing blades have maximum lift in the areas swept out by the outer blade lengths (the outer approximately 25 percent of area swept out), a median lift area in the centrally swept out areas, and a non-effective lift region in the area swept out by the shorter blade lengths. The vertical lift system approach taught in the present vector rotary wing ensemble (VRWE) invention admirably overcomes these and other disadvantages of the prior art approaches, and provides a significant improvement to the field of vertical aerodynamic lift.